It is well known that magnetic layers are superimposed upon each other to increase the electromagnetic characteristics of a magnetic recording medium.
When a magnetic recording medium comprising plural magnetic layers is used, upper and lower magnetic layers can differ from each other in coercive force (Hc), residual magnetic flux density (Br), or the size of magnetic particles (which is represented by crystallite size or specific surface area). As a result, output at a wide range of frequencies increases, thereby improving electromagnetic characteristics. See, for example, in JP-A-52-51908 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-54-21304, JP-A-54-48504, JP-A-58-56228, JP-A-58-56229, and JP-A-53-54002.
However, magnetic recording media, such as an audio tape, a video tape, or a magnetic disk, now require higher density recording, higher output, and lower noise. Therefore, even if a magnetic tape comprising plural magnetic layers is used, the electromagnetic characteristics of it are insufficient.
JP-A-54-48504 shows that the coercive force (Hc) of the second magnetic layer (i.e., upper magnetic layer) is 590 to 800 Oe (which corresponds to 4.7.times.10.sup.4 A/m to 6.4.times.10.sup.4 A/m), the residual magnetic flux density (Br) is 1200 gauss or more (which corresponds to 1.2.times.10.sup.-1 wb/m.sup.2 or more), a ratio of Br/Hc is 2.55.times.10.sup.-6 H/m or more, and the coercive force of the first magnetic layer is 400 to 560 Oe (which corresponds to 3.18.times.10.sup.4 A/m to 4.45.times.10.sup.4 A/m). However, with such a combination of parameters, chroma output and S/N ratio increase, whereas RF output and YS/N ratio are insufficient. This is because the Hc value in magnetic recording media comprising plural magnetic layers is insufficient for high density recording; even if Hc is increased, packing density is low, and sufficient output cannot be obtained; even if the particle size in an upper magnetic layer is small, surface property threof is insufficient, and the reduction of noise is insufficient; if the thickness of an upper magnetic layer is thick, the effects due to plural magnetic layers are difficult to obtain; and if magnetic characteristics of upper and lower magnetic layers are not appropriate for the magnetic field of a magnetic head, for example, if Hc of a lower magnetic layer is too high, the recording is insufficient.
The present inventors have made extensive studies and consequently discovered a magnetic recording medium having excellent electromagnetic characteristics.